1. Field of the Invention
The present invention relates to a method for determining crystal orientation, and more particularly to improvement in a method which utilize polarization selective Raman microprobe spectroscopy.
2. Description of the Prior Art
Raman microprobe determination of crystal orientation is described, e.g., in Appl. Phys. Lett., vol. 44, 1984, pp. 535-537 by J. B. Hopkins et al. and J. Appl. Phys., vol. 59, 1986, pp. 1103-1110 by J. B. Hopkins et al.
The Raman scattering intensity I is expressed by the following formula: ##EQU1## where e.sub.1 and e.sub.2 are the polarization vectors of the incident light and the scattered light respectively, and R.sup.j represents a Raman tensor.
Referring to FIG. 1, there is shown a conceptional perspective view illustrating the geometrical relation between the polarizations of incident light and scattered light. Incident light 1 is focused on a specimen 5 of silicon or the like, and Raman scattered light 3 is emitted from the crystal 5. On this occasion, the incident light 1 has a polarization direction 2 which is rotated by a polarization angle .psi..sub.1, from a reference .psi..sub.0, while the Raman scattered light 3 has a polarization direction 4 which is rotated by a polarization angle .psi..sub.2 from the same reference .psi..sub.0. The scattered light 3 having this polarization direction 4 is selected by a polarization analyzer and the intensity I of the selected light 3 is measured. A series of the intensity measurements represents the polarization characteristic which reflects the crystal orientation. The geometrical relation between the incident light beam 1 and the crystal axes &lt;100&gt; can be determined by fitting a measured intensity profile of the scattered light 3 taken as a function of the polarization angles to that derived from the formula (1) as to known crystal orientation.
Referring to FIG. 2, there is shown a block diagram of an apparatus for determining crystal orientation. A laser beam 12 emitted from a laser source 11 is passed through a spectroscopic filter 13 and the natural light is eliminated. The polarization direction of the filtered beam 12 is controlled by a polarizer 14 and then the beam 12 is expanded by a beam expander 15. The expanded beam is deflected by a half mirror 16 and focused by a lens 17 on a specimen 5 of which crystal orientation is to be determined. At this time, light having spectroscopic energies different from that of the original laser beam 12 is emitted as Raman scattered light from the specimen 5. The Raman scattered light 19 is collected by the lens 17 and deflected by a mirror 20 toward a polarization analyzer 21 in which light having a predetermined polarization direction is selected. The selected Raman scattered light is passed through a depolarizer 22 and focused by a lens 23 on a slit of a spectrometer 24. Spectra separated in the spectrometer 24 are detected by a photodetector 25, and then obtained data are processed by a computer 26 thereby to determine crystal orientation.
During measurements with this apparatus, the polarization direction of only either one of the incident light and the scattered light is systematically varied by correspondingly rotating only either one of the polarizer 14 and the polarization analyzer 21 with the other being fixed. Thus, it takes a long time to analyze the data, and the crystal orientation can not be determined three-dimensionally by one series of the measurements.